MirOS Manual: Benchmark(3p)


Benchmark(3p)   Perl Programmers Reference Guide    Benchmark(3p)

NAME

     Benchmark - benchmark running times of Perl code

SYNOPSIS

         use Benchmark qw(:all) ;

         timethis ($count, "code");

         # Use Perl code in strings...
         timethese($count, {
             'Name1' => '...code1...',
             'Name2' => '...code2...',
         });

         # ... or use subroutine references.
         timethese($count, {
             'Name1' => sub { ...code1... },
             'Name2' => sub { ...code2... },
         });

         # cmpthese can be used both ways as well
         cmpthese($count, {
             'Name1' => '...code1...',
             'Name2' => '...code2...',
         });

         cmpthese($count, {
             'Name1' => sub { ...code1... },
             'Name2' => sub { ...code2... },
         });

         # ...or in two stages
         $results = timethese($count,
             {
                 'Name1' => sub { ...code1... },
                 'Name2' => sub { ...code2... },
             },
             'none'
         );
         cmpthese( $results ) ;

         $t = timeit($count, '...other code...')
         print "$count loops of other code took:",timestr($t),"\n";

         $t = countit($time, '...other code...')
         $count = $t->iters ;
         print "$count loops of other code took:",timestr($t),"\n";

         # enable hires wallclock timing if possible
         use Benchmark ':hireswallclock';

perl v5.8.8                2005-02-05                           1

Benchmark(3p)   Perl Programmers Reference Guide    Benchmark(3p)

DESCRIPTION

     The Benchmark module encapsulates a number of routines to
     help you figure out how long it takes to execute some code.

     timethis - run a chunk of code several times

     timethese - run several chunks of code several times

     cmpthese - print results of timethese as a comparison chart

     timeit - run a chunk of code and see how long it goes

     countit - see how many times a chunk of code runs in a given
     time

     Methods

     new       Returns the current time.   Example:

                   use Benchmark;
                   $t0 = new Benchmark;
                   # ... your code here ...
                   $t1 = new Benchmark;
                   $td = timediff($t1, $t0);
                   print "the code took:",timestr($td),"\n";

     debug     Enables or disable debugging by setting the
               $Benchmark::Debug flag:

                   debug Benchmark 1;
                   $t = timeit(10, ' 5 ** $Global ');
                   debug Benchmark 0;

     iters     Returns the number of iterations.

     Standard Exports

     The following routines will be exported into your namespace
     if you use the Benchmark module:

     timeit(COUNT, CODE)
               Arguments: COUNT is the number of times to run the
               loop, and CODE is the code to run.  CODE may be
               either a code reference or a string to be eval'd;
               either way it will be run in the caller's package.

               Returns: a Benchmark object.

     timethis ( COUNT, CODE, [ TITLE, [ STYLE ]] )
               Time COUNT iterations of CODE. CODE may be a
               string to eval or a code reference; either way the
               CODE will run in the caller's package. Results

perl v5.8.8                2005-02-05                           2

Benchmark(3p)   Perl Programmers Reference Guide    Benchmark(3p)

               will be printed to STDOUT as TITLE followed by the
               times. TITLE defaults to "timethis COUNT" if none
               is provided. STYLE determines the format of the
               output, as described for timestr() below.

               The COUNT can be zero or negative: this means the
               minimum number of CPU seconds to run.  A zero sig-
               nifies the default of 3 seconds.  For example to
               run at least for 10 seconds:

                       timethis(-10, $code)

               or to run two pieces of code tests for at least 3
               seconds:

                       timethese(0, { test1 => '...', test2 => '...'})

               CPU seconds is, in UNIX terms, the user time plus
               the system time of the process itself, as opposed
               to the real (wallclock) time and the time spent by
               the child processes.  Less than 0.1 seconds is not
               accepted (-0.01 as the count, for example, will
               cause a fatal runtime exception).

               Note that the CPU seconds is the minimum time: CPU
               scheduling and other operating system factors may
               complicate the attempt so that a little bit more
               time is spent.  The benchmark output will, how-
               ever, also tell the number of $code runs/second,
               which should be a more interesting number than the
               actually spent seconds.

               Returns a Benchmark object.

     timethese ( COUNT, CODEHASHREF, [ STYLE ] )
               The CODEHASHREF is a reference to a hash contain-
               ing names as keys and either a string to eval or a
               code reference for each value. For each (KEY,
               VALUE) pair in the CODEHASHREF, this routine will
               call

                       timethis(COUNT, VALUE, KEY, STYLE)

               The routines are called in string comparison order
               of KEY.

               The COUNT can be zero or negative, see timethis().

               Returns a hash of Benchmark objects, keyed by
               name.

     timediff ( T1, T2 )

perl v5.8.8                2005-02-05                           3

Benchmark(3p)   Perl Programmers Reference Guide    Benchmark(3p)

               Returns the difference between two Benchmark times
               as a Benchmark object suitable for passing to
               timestr().

     timestr ( TIMEDIFF, [ STYLE, [ FORMAT ] ] )
               Returns a string that formats the times in the
               TIMEDIFF object in the requested STYLE. TIMEDIFF
               is expected to be a Benchmark object similar to
               that returned by timediff().

               STYLE can be any of 'all', 'none', 'noc', 'nop' or
               'auto'. 'all' shows each of the 5 times available
               ('wallclock' time, user time, system time, user
               time of children, and system time of children).
               'noc' shows all except the two children times.
               'nop' shows only wallclock and the two children
               times. 'auto' (the default) will act as 'all'
               unless the children times are both zero, in which
               case it acts as 'noc'. 'none' prevents output.

               FORMAT is the printf(3)-style format specifier
               (without the leading '%') to use to print the
               times. It defaults to '5.2f'.

     Optional Exports

     The following routines will be exported into your namespace
     if you specifically ask that they be imported:

     clearcache ( COUNT )
               Clear the cached time for COUNT rounds of the null
               loop.

     clearallcache ( )
               Clear all cached times.

     cmpthese ( COUNT, CODEHASHREF, [ STYLE ] )
     cmpthese ( RESULTSHASHREF, [ STYLE ] )
               Optionally calls timethese(), then outputs com-
               parison chart.  This:

                   cmpthese( -1, { a => "++\$i", b => "\$i *= 2" } ) ;

               outputs a chart like:

                          Rate    b    a
                   b 2831802/s   -- -61%
                   a 7208959/s 155%   --

               This chart is sorted from slowest to fastest, and
               shows the percent speed difference between each
               pair of tests.

perl v5.8.8                2005-02-05                           4

Benchmark(3p)   Perl Programmers Reference Guide    Benchmark(3p)

               c<cmpthese> can also be passed the data structure
               that timethese() returns:

                   $results = timethese( -1, { a => "++\$i", b => "\$i *= 2" } ) ;
                   cmpthese( $results );

               in case you want to see both sets of results.

               Returns a reference to an ARRAY of rows, each row
               is an ARRAY of cells from the above chart, includ-
               ing labels. This:

                   my $rows = cmpthese( -1, { a => '++$i', b => '$i *= 2' }, "none" );

               returns a data structure like:

                   [
                       [ '',       'Rate',   'b',    'a' ],
                       [ 'b', '2885232/s',  '--', '-59%' ],
                       [ 'a', '7099126/s', '146%',  '--' ],
                   ]

               NOTE: This result value differs from previous ver-
               sions, which returned the "timethese()" result
               structure.  If you want that, just use the two
               statement "timethese"..."cmpthese" idiom shown
               above.

               Incidently, note the variance in the result values
               between the two examples; this is typical of
               benchmarking.  If this were a real benchmark, you
               would probably want to run a lot more iterations.

     countit(TIME, CODE)
               Arguments: TIME is the minimum length of time to
               run CODE for, and CODE is the code to run.  CODE
               may be either a code reference or a string to be
               eval'd; either way it will be run in the caller's
               package.

               TIME is not negative.  countit() will run the loop
               many times to calculate the speed of CODE before
               running it for TIME.  The actual time run for will
               usually be greater than TIME due to system clock
               resolution, so it's best to look at the number of
               iterations divided by the times that you are con-
               cerned with, not just the iterations.

               Returns: a Benchmark object.

     disablecache ( )
               Disable caching of timings for the null loop. This

perl v5.8.8                2005-02-05                           5

Benchmark(3p)   Perl Programmers Reference Guide    Benchmark(3p)

               will force Benchmark to recalculate these timings
               for each new piece of code timed.

     enablecache ( )
               Enable caching of timings for the null loop. The
               time taken for COUNT rounds of the null loop will
               be calculated only once for each different COUNT
               used.

     timesum ( T1, T2 )
               Returns the sum of two Benchmark times as a Bench-
               mark object suitable for passing to timestr().

     :hireswallclock

     If the Time::HiRes module has been installed, you can
     specify the special tag ":hireswallclock" for Benchmark (if
     Time::HiRes is not available, the tag will be silently
     ignored).  This tag will cause the wallclock time to be
     measured in microseconds, instead of integer seconds.  Note
     though that the speed computations are still conducted in
     CPU time, not wallclock time.

NOTES

     The data is stored as a list of values from the time and
     times functions:

           ($real, $user, $system, $children_user, $children_system, $iters)

     in seconds for the whole loop (not divided by the number of
     rounds).

     The timing is done using time(3) and times(3).

     Code is executed in the caller's package.

     The time of the null loop (a loop with the same number of
     rounds but empty loop body) is subtracted from the time of
     the real loop.

     The null loop times can be cached, the key being the number
     of rounds. The caching can be controlled using calls like
     these:

         clearcache($key);
         clearallcache();

         disablecache();
         enablecache();

     Caching is off by default, as it can (usually slightly)
     decrease accuracy and does not usually noticably affect

perl v5.8.8                2005-02-05                           6

Benchmark(3p)   Perl Programmers Reference Guide    Benchmark(3p)

     runtimes.

EXAMPLES

     For example,

         use Benchmark qw( cmpthese ) ;
         $x = 3;
         cmpthese( -5, {
             a => sub{$x*$x},
             b => sub{$x**2},
         } );

     outputs something like this:

        Benchmark: running a, b, each for at least 5 CPU seconds...
               Rate    b    a
        b 1559428/s   -- -62%
        a 4152037/s 166%   --

     while

         use Benchmark qw( timethese cmpthese ) ;
         $x = 3;
         $r = timethese( -5, {
             a => sub{$x*$x},
             b => sub{$x**2},
         } );
         cmpthese $r;

     outputs something like this:

         Benchmark: running a, b, each for at least 5 CPU seconds...
                  a: 10 wallclock secs ( 5.14 usr +  0.13 sys =  5.27 CPU) @ 3835055.60/s (n=20210743)
                  b:  5 wallclock secs ( 5.41 usr +  0.00 sys =  5.41 CPU) @ 1574944.92/s (n=8520452)
                Rate    b    a
         b 1574945/s   -- -59%
         a 3835056/s 144%   --

INHERITANCE

     Benchmark inherits from no other class, except of course for
     Exporter.

CAVEATS

     Comparing eval'd strings with code references will give you
     inaccurate results: a code reference will show a slightly
     slower execution time than the equivalent eval'd string.

     The real time timing is done using time(2) and the granular-
     ity is therefore only one second.

     Short tests may produce negative figures because perl can
     appear to take longer to execute the empty loop than a short

perl v5.8.8                2005-02-05                           7

Benchmark(3p)   Perl Programmers Reference Guide    Benchmark(3p)

     test; try:

         timethis(100,'1');

     The system time of the null loop might be slightly more than
     the system time of the loop with the actual code and there-
     fore the difference might end up being < 0.

SEE ALSO

     Devel::DProf - a Perl code profiler

AUTHORS

     Jarkko Hietaniemi <jhi@iki.fi>, Tim Bunce
     <Tim.Bunce@ig.co.uk>

MODIFICATION HISTORY

     September 8th, 1994; by Tim Bunce.

     March 28th, 1997; by Hugo van der Sanden: added support for
     code references and the already documented 'debug' method;
     revamped documentation.

     April 04-07th, 1997: by Jarkko Hietaniemi, added the run-
     for-some-time functionality.

     September, 1999; by Barrie Slaymaker: math fixes and accu-
     racy and efficiency tweaks.  Added cmpthese().  A result is
     now returned from timethese().  Exposed countit() (was run-
     for()).

     December, 2001; by Nicholas Clark: make timestr() recognise
     the style 'none' and return an empty string. If cmpthese is
     calling timethese, make it pass the style in. (so that
     'none' will suppress output). Make sub new dump its debug-
     ging output to STDERR, to be consistent with everything
     else. All bugs found while writing a regression test.

     September, 2002; by Jarkko Hietaniemi: add ':hireswallclock'
     special tag.

     February, 2004; by Chia-liang Kao: make cmpthese and timestr
     use time statistics for children instead of parent when the
     style is 'nop'.

perl v5.8.8                2005-02-05                           8

Generated on 2014-07-04 21:17:45 by $MirOS: src/scripts/roff2htm,v 1.79 2014/02/10 00:36:11 tg Exp $

These manual pages and other documentation are copyrighted by their respective writers; their source is available at our CVSweb, AnonCVS, and other mirrors. The rest is Copyright © 2002‒2014 The MirOS Project, Germany.
This product includes material provided by Thorsten Glaser.

This manual page’s HTML representation is supposed to be valid XHTML/1.1; if not, please send a bug report – diffs preferred.